The present invention relates to a 3-dimensional wave-guiding structure for use in horn-type or tube-type waveguides to guide electromagnetic waves in high frequency range, particularly in extremely high frequency range.
Heretofore, a horn or tube-type waveguide has been made of metal to provide electrical characteristics therein. The shape of the waveguide should be exactly maintained in its entirety to allow electromagnetic waves to be effectively guided along a 3-dimensional channel formed therein. If the waveguide is made only of metal to assure adequate strength/rigidity for the above purpose, the waveguide will inevitably have an excessively increased weight, which leads to deteriorated operationality in a large-size movable waveguide such as double-ridge guide horn antennas. Thus, it has been desired to achieve weight reduction in the waveguide. In particular, the severe lightweight requirement of space satellites has not been ever impossible to be cleared by the conventional metal waveguide.
Recently, it has been developed a new laminated structure prepared by adhesively attaching a metal film such as a metallic foil onto a fiber-reinforced composite material or by plating a certain metal over the fiber-reinforced composite material to achieve the structural strength/rigidity by the lightweight composite material and provide the electrical characteristics by a metal layer formed thereon.
According to this laminated structure, a lightweight waveguide with excellent electrical characteristics can be theoretically obtained while assuring and maintaining the shape/mechanical strength and the electrical characteristics required for horn or tube-type waveguides by the composite material and the metal layer, respectively.
However, when a certain metal is plated on the surface of the composite material formed in a given shape, it is actually difficult to plate the metal uniformly over the composite material and form a metal layer with an even thickness, particularly in a waveguide having a 3-dimensional complicated shape, because the shaped composite material generally has an extremely large surface area, while a processing bath or chamber is practically limited in volume irrespective of whether the plating is a wet or dry processing. In addition, if the metal layer is formed through a wet plating process, the composite material can be undesirably corroded by a plating solution, or the plating solution can be undesirably absorbed in the composite material.
In the structure prepared by adhesively attaching or laminating a metal film onto the composite material, the composite material and the metal film are not always attached together with a sufficient adhesive or cohesive force. Thus, the laminated structure can be deformed due to mechanical load, or the metal film can be peeled off due to strong vibrations. In addition, the deterioration of the cohesive force inevitably causes the peeling of the metal film.
Further, when a metal film is adhesively attached onto the composite material formed as a horn or tube-type waveguide including 3-dimensionally curved surfaces along its channel for guiding electromagnetic waves, the metal film cannot be shaped in conformity to the 3-dimensionally curved surfaces in advance. Thus, an electrically continuity has been hardly maintained over the entire 3-dimensionally curved surfaces through the technique of adhesively attaching the metal film.
In particular, a plenty of waveguide components, such as a waveguide diplexer, waveguide circulator, hybrid waveguide and waveguide directional coupler, are provided with a 3-dimensional hollow structure which serves as a channel for guiding electromagnetic waves and includes bent and branched portions having 3-dimensionally curved surfaces. Therefore, the waveguide prepared through the above conventional technique has a limited range of applications.
In view of the above problems, it is therefore an object of the present invention to provide a wave-guiding structure capable of assuring excellent electrical characteristics required for horn or tube-type waveguides while maintaining desired mechanical strength in combination with a composite material.
In order to achieve this object, according to a first aspect of the present invention, there is provided a 3-dimensional wave-guiding structure for horn or tube-type waveguides, comprising a fiber-reinforced composite material and a conductive nonwoven fabric shaped together with the composite material.
According to a second aspect of the present invention, there is provided a 3-dimensional wave-guiding structure for horn or tube-type waveguides, comprising a conductive nonwoven fabric and a fiber-reinforced triaxial woven fabric which are laminated alternately or in an arbitrary order and shaped together.
In the present invention, a horn or tube-type waveguide can be formed by laminating a fiber-reinforced composite material and a conductive nonwoven fabric together to provide a desired mechanical strength by the composite material and assure electrical characteristics required for the waveguide structure by the conductive nonwoven fabric. The laminated structure may be obtained by laminating a conductive nonwoven fabric and a pre-preg comprising a resin-impregnated fiber-reinforced woven fabric alternately or in an arbitrary order or combination, attaching them together under heat and compression, and shaping them together.
The conductive nonwoven fabric is formed by combing fine fibers. The resulting flexibility allows the conductive nonwoven fabric to be readily formed in a complicated shape for a horn or tube-type waveguides while maintaining its mesh structure. In addition, the mesh structure allows the conductive nonwoven fabric to be impregnated commonly with the resin impregnated in the fiber-reinforced composite material so as to form an integral structure. For example, in a laminated structure including the conductive nonwoven fabric sandwiched between the fiber-reinforced pre-pregs, the conductive nonwoven fabric can be sufficiently integrated with the fiber-reinforced pre-pregs disposed on the front and back surfaces thereof. Thus, even in a laminated structure having plural sets of such laminated layers, a desirable strength can be maintained without any peeling of the layers.
The conductive nonwoven fabric may be a nonwoven fabric comprising metal fibers or metallized fibers, or a metallized nonwoven fabric obtained by depositing metal on a nonwoven fabric. The electrical characteristics, such as conductivity, required for horn or tube-type waveguides, may be achieved by selecting the type of the metal or the diameter of the fiber or by adjusting the density the conductive nonwoven fabric based on the porosity or thickness thereof depending on electromagnetic wavelength to be guided.
While the fiber-reinforced composite material is not limited to a specific structure, it preferably comprises a fiber-reinforced woven fabric, more preferably a fiber-reinforced triaxial woven fabric, to provide an accurate horn or tube-type waveguide having anisotropy in mechanical characteristics and/or thermal expansion without distortion otherwise caused during shaping process.
The laminated structure may be a symmetrically laminated structure including one or more conductive nonwoven fabrics, such that the triaxial woven fabric/the conductive nonwoven fabric/the triaxial woven fabric, or the conductive nonwoven fabric/the triaxial woven fabric/the conductive nonwoven fabric are laminated in this order. The structure having the nonwoven fabric sandwiched between the triaxial woven fabrics can minimize thermal distortion to be caused in the laminated structure. The conductive nonwoven fabric can be sandwiched between appropriate triaxial woven fabrics to provide a high cohesive strength therebetween.
The textured structure of the triaxial woven fabric has hexagonal through-holes penetrating the front and back surfaces of the structure. The triaxial woven fabric can be texturized so as to adjust the respective sizes of the through-holes to provide an electrical conduction between the conductive nonwoven fabrics sandwiching the triaxial woven fabric on its front and back surfaces. According to the above structure, both mechanical and electrical characteristic can be adjustably improved by stacking up an appropriate number of the fiber-reinforced triaxial woven fabrics and the conductive nonwoven fabrics.
The conductive nonwoven fabric has flexibility allowing it to be handled as with the fiber-reinforced pre-preg. Thus, the process of attaching the conductive nonwoven fabric and the composite material under heat and compression to form a horn or tube-type waveguide may be used any commonly used method in the field of fiber-reinforced composite materials.